1. Technical Field
The present invention relates to digital data distribution, such as a digital satellite broadcast or other multimedia content communication, and in particular to distributing digital data comprised of computer language commands defining data attributes. The computer language commands are represented, for example, in the form of data that is divided by tags that define the data attribute, known as a “markup language”.
Further, the present invention relates to the distributing of data content in a language that uses arbitrarily definable tags, such as XML (eXtensible Markup Language), within the data broadcast and to the receiving and displaying of the content. In particular, the invention relates to the distributing and selecting of style sheets for prescribing the expression format of XML instances or XSL (eXtensible Style sheet Language) documents.
2. Background Art
In the field of broadcasting, the use of digital data is rapidly growing. Digital signals are superior to analog signals because of their stability and the higher compressibility of the data. Further, digital signals, whether sent over a cable, a ground wave or a satellite wave, provide more channels than analog signals for certain bands. In addition, though various information, such as documents, voice data and picture data are separated in a conventional transmission, the digitized broadcast data enables transmission of these monomedia data types indiscriminately.
For example, using a digital broadcast, improved service is provided to users (i.e., viewers) by sending EPG (Electric Program Guide) and other system information as part of the data broadcast content together with the image and voice information. The EPG may include the capability of video recording, in addition to providing a broadcast schedule, a name of broadcast programs and other information.
Data delivered in a digital format has a high compatibility with general-purpose computer systems and with other non-television information equipment. For example, a general-purpose computer system may be equipped with a tuner card for satellite broadcasts to parse the EPG data received in the computer, process the same for display, and display program tables and other menu screens in a window. Using such a menu screen, it is possible to switch programs and reserve video recordings by moving a mouse controlled cursor or using a touch panel. Moreover, it is possible to store the received data broadcast content on a hard disc, that is integrated with the computer, to be reproduced or reused.
Moreover, using a digital broadcast, it is possible to enhance the interaction of broadcast programs by taking advantage of the band used and by transmitting data other than the image and voice broadcast programs. For example, in a broadcast program in which true-false quizzes are given, the transmission of answers as well as image and voice data enables the satellite TV broadcast receivers (i.e., viewers) to use answer menu buttons on the computer display and to check the answers by means of the mouse cursor or the touch panel.
When the interaction is further enhanced, home TV receivers may play an active role as an information controller to handle more than image content. For example, a TV receiver may serve as an Internet terminal or as an electronic commerce terminal.
In Japan, the ARIB (Association of Radio Industries and Businesses) is playing a central role in promoting standardization of the digital satellite data broadcast. Using the digital satellite broadcast, digital transfer data supplementary to the broadcast program is distributed, in addition to the image and voice data constituting the main body of the broadcast program (AV data). More specifically, data is transmitted as broadcast waves in the form of a transport stream obtained by multiplexing the AV data compressed by a specified compression method, such as the MPEG (Motion Picture Experts Group) 2 format, with digital transfer data.
An example of broadcast program information transmitted as data broadcast content is the aforementioned EPG (Electric Program Guide). Information inherent to the main body of the broadcast program may be included, such as the title and date of the broadcast program as well as the program casting. The types of and the construction of the data contained in the broadcast program information are systematized to some extent in accordance with the service content provided by the main body of the program. For example, information related to recipes and food materials may be delivered with a cooking program, the number of votes cast may be obtained and renewed constantly and then delivered in a real-time report of election returns, and the individual batting and pitching records of various players and the team rankings may be delivered with a professional baseball game broadcast.
Broadcast program information is typically displayed using part of the same display screen of the receiving system that displays the main body of the broadcast program. The receiving system typically includes a receiver for receiving, tuning and decoding the broadcast wave, such as a set top box (STB) and a television (TV) set for displaying/outputting the broadcast. The receiving system is typically installed in the home of a viewer.
The construction of content distributed as digital broadcast data, hereinafter referred to as “data broadcast content”, is explained by referring to FIG. 1.
As shown in FIG. 1, the data broadcast content consists of a large variety of monomedia data including text data, still pictures, animation images, voice data, etc., as well as a display and output control program that prescribes the state of broadcast program information by handling integrally each of the monomedia data or multimedia data, generally referred to as a multimedia coding application. It is possible to integrate information corresponding to the monomedia information to the display output control program.
As part of the standardization of the digital satellite data broadcast undertaken by the aforementioned ARIB, a first attempt at a format for describing the multimedia coding applications of data broadcast content used MHEG (Multimedia and Hypermedia Expert Group). MHEG is a descriptive language that defines data attributes and displays multimedia content on TVs and which is designed to allow viewers to obtain their desired information from Video On Demand (VOD) or digital TV broadcast. MHEG-5 is already used in the Japanese CS (Communication Satellite) digital broadcast known as SKY Perfect TV.
MHEG, however, uses a fixed coding space and lacks extensibility. In other words, a unilaterally fixed coding space must be used to describe a change of a single function. For example, an API (Application Programming Interface) requires a considerable amount of correction work. In addition, MHEG is generally not well known, and thus data content written in MHEG is not circulated in a sufficient quantity. In this sense, MHEG has a relatively low applicability for general-purpose computers.
As a result, the ARIB is examining standardization based on XML (eXtensible Markup Language) in place of MHEG. More specifically, work is progressing in dividing content into “basic XML”, also referred to as BML (“Broadcast Markup Language”), and “advanced XML”, an extended version of the basic XML.
XML allows for the optional definition of tags and has no restrictions on the way attributes are described. XML therefore allows a high degree of freedom and its high applicability in general-purpose computers and the Internet provides advantages over MHEG. Furthermore, XML is now being developed as a descriptive language for the next generation of the Internet.
When XML is used as the standard language of data broadcast content, it is possible to exchange data for digital broadcast among a variety of information equipment, such as computers, TVs, telephones, etc. In addition, as XML can be used to freely define tag attributes, it is more suitable for data processing than HTML (Hyper Text Markup Language). Consequently, its use is rapidly expanding in various fields including electronic commerce.
Document files written in XML format are called “XML instances.” The writing of attribute information (or tag grammar) is governed by a standard known as DTD (Document Type Definition). For example, a DTD may be established for every industry or for every service provided by each industry.
XML instances themselves do not always contain the style information on the form expressed, such as the form of the output to displays or the form of the output to printers, etc. In this case, the expression of the XML instances is described by a “style sheet” or a document file different from DTD.
The style sheet for XML instances can be written by using particular languages, such as in the form of XSL (eXtensible Style sheet Language), CSS (Cascade Style Sheet), XSLT (XSL Transformation) or a standard derived from the abovementioned. Alternatively, a script may be inserted into a style sheet. A script is a method of executing software described in a text form in the same manner as ordinary source programs. A script is used to automate a series of processes resulting from the combination of operating procedures that users can control, such as specific keys or buttons, in an application or in an OS (Operating System).
Even when XML instances are the same, depending on the description in the style sheet concerned, the same XML instance may be expressed on the display screen in a completely different form by varying the font style, size or color. In other words, a style sheet has the function of providing added information to the original XML instance. It can be assumed that the importance of style sheets will grow in the future as more attractive style sheets are designed by specialized designers.
Style sheets can be transmitted in a file separate from that storing the XML instance. For example, XML instances may be distributed by data broadcast, whereas the style sheets may be distributed using other forms of distribution, for example, using portable recording media such as a CD (Compact Disc), an MO (Magneto-Optical) disc, a DVD (Digital Versatile Disc) or by file transfers through the Internet.
Meanwhile, the choice of display apparatus that can output the data broadcast content are becoming more diverse. For example, in addition to the conventional NTSC (National Television System Committee) color television systems, HDTV (High Definition Television) systems with many scanning lines for large screens, PDA (Personal Digital Assistant) devices with a monochrome liquid crystal display of a small screen size, and relatively high definition computer screens such as SVGA (Super Video Graphic Array) or XGA (eXtended Graphic Array) are under development.
Thus, though the data content may be the same, when the display capacity of the output device is different, the optimum form of the display is different. For example, a display format that is optimum for a high resolution, high definition HDTV is not necessarily appropriate for a low resolution, small screen PDA. As mentioned earlier, the format used for expressing content is defined by style sheets. Therefore, the style sheet that is appropriate for such content is determined by the display and output capacity and expression capacity of the display apparatus to which the data content is outputted.
Also, even when the resolution and other hardware capacity for the display apparatus are identical, the optimum format of display may differ depending on the manufacturer and the type of apparatus used.
In addition, depending on the attribute of data broadcast content, for example, depending on the data shown by the tags <POSITION>, <COLOR>, <SIZE>, etc., the optimum choice of style sheet may differ.
Further, the optimum style sheets or the style sheets most preferred by the receiving user are not always distributed together with the data broadcast content.